Australian Patent Application No. 46168/72 describes a splitter having a blade extending vertically and mounted for rotation about an upright pivotal axis in relation to a conical or cylindrical take-off in the floor of the sluice with the vertical blade diverting adjustable proportions of concentrate into the take-off. Such devices have the disadvantage that the maximum adjustment range is limited by the necessarily planar face to the top of the take-off where the splitter rotates and the incorporation of such a planar surface into the floor of the helical sluice causes severe distortion to the normal shape of the latter with consequent flow distortion if the take-off is of excessive diameter. In this case also, the protruding splitter blade causes severe flow disturbance when rotated to a position such that little or no concentrate is taken.
In some separators the blade is mounted for translation in a radial direction as is described in Australian Patent Number 522914. Other separators have been provided with a splitter blade which is mounted for rotation about an axis normal to the floor of the volute, that is to say substantially parallel to the axis of the volute. In such cases the position of separation is adjusted by rotating the splitter blade about its axis. A portion of the splitter blade upstream of the axis, upon rotation, traverses the volute, and so adjustment is achieved.
A plurality of splitters have previously been used in spiral separators wherein a pair of splitter blades are positioned side-by-side at the bottom of the sluice wherein a concentrate/middlings splitter is positioned in the inner part of the sluice and a middling/tailings splitter is positioned adjacent to but further outward in the same radial area of the sluice with particles of high density being referred to as concentrates, of intermediate density as middlings and of low density as tailings although high or low density fractions may be the valuable compound. Such an arrangement is shown in Australian Pat. No. 536,090 by Douglas Charles Wright. The splitter blades operate side-by-side as shown in FIG. 1 of that patent specification and this avoids flow interaction between the two splitter blades. However this also results in some limitations in the effective range over which each splitter blade may be adjusted. The problem is that the arcs of movement of the splitter blades may not overlap since the shapes of the surfaces on which the splitters seat on the sluice conflict.